By

Mr. Sombat Chuenchooklin

Application of geographic information systems for flood extent

determination in floodplain

: a case study in the Yom River Basin in Phichit Province

Working group: CGIST at Lower-Northern Regional Office,

Phitsanulok

E-mail: sombatc@nu.ac.th

Department of Civil Engineering, Faculty of Engineering, Naresuan University, Phitsanulok 65000 Thailand

Introduction• Determination of flood extent in floodplain is difficult

due to flat topography and there are many obstructs.

• By using hydrologic & hydraulic principles incorporated to physical characteristics, flood can be estimated.

• Those basins characteristics can be found as existing database presented by GIS.

• Those data included some attributed data which has been digitized from aerial map i.e. roads, streams, water sources, wetlands, contour-lines, land-uses, soil series, rainfall-gauges, and local administration boundary as well as location of villages.

Objectives of the study

• To use of some existing data and data generation using GIS techniques to generate some basically parameters in the Hydrological Model based on limit data.

• To compute flood volume and inundated extent in the floodplain area in ungauged basin for a given period using appropriate techniques in hydrologic & hydraulic models.

Steps to estimate flood extensive in river floodplain

Input data

Process

Output

-GIS, topographic map & basically data-Basin characteristics, streams, slope-Soil & vegetative cover, land-use-Cross-sectional profile of floodplain & main streams-Rainfall data from rain gauges in basin-Meteorological data, max-min temperature, etc.

-Draw sub-basin characteristics & contours-Generate rainfall isohyets, ET using ArcView GIS-Compute surface runoff, traveling time from each sub-basin to floodplain using appropriate hydrology techniques i.e. synthetic unit hydrograph using Gamma function-Calculate over-bank flow from river to floodplain using river hydraulic analysis model (HEC, 2001)-Estimate inundated volume & extent boundary

Flood volume & extensive map

Materials & Methods

Model design as water balance budget in study area:- Water budget for the study area becomes the following continuity equation: {Qsimup(t)+Qin1(t)+Qin2(t)+Qin3(t)+Qo(t)-Qsimout(t)}+P(t).A–ET(t).A-I(t).A=V(t,H) (1) Whereas:• : daily river flow at up/downstream boundaries in MCM,• Qin:daily inflow volume of all side-flows at boundary i=1….n, in MCM,• Qo:daily overtop-bank flow from river j=1....m, in MCM,• Qout: daily outflow measured from road structures at boundary k=1...r,• P:mean daily rainfall in mm,• E:daily evaporation from lakes,ponds and inundated area in mm,• ETc:daily crop water requirement calculated from ETc=Kc.ET in mm,• Kc:crop coefficient for each crop stage,• ET:Potential evapotranspiration in mm,• I:mean daily infiltration rate in mm,• Ac:area with crops in sq.km,• Af: inundated area in sq.km,• : change in daily storage volume in MCM.

upsimQdssimQ

V

Hydrological studying

Kaengsuaten dam site

Maeyom weir Maesong

Maethang

ThaphaeExisting Project

RoadStreamIrrigable

area

SUKHOTHAI

PRAE

PHITSANULOKPHICHIT

KAMPAENGPHET

NAKHONSAWAN

Nan

Nan

Wan

gW

ang

Pin

gP

ing

ChaophyaChaophyaCentral Plain Rice’s Bowl

Yom

Yom

Pas

akP

asak

Sakaekrang

Sakaekrang

En

larg

er o

f th

e Y

om

Bas

in Study area & Chaophya R. Basin

Thajean

Thajean

Maeklong

Maeklong

Ban

gpra

kong

Ban

gpra

kong

Study area

Existing database in the Yom R. & its catchments– Area of 1,705 sq.km. in Kampaengphet & Phichit.– Flat sloping land lay from west to east & north to south

ranging from 0.0001 to 0.0005.– There are 7 sub-basins divided with average size of 41.18

sq.km, average stream length of 7.893 km.– Most side-flow runoff comes from the west via

Kampaengphet to the Yom R. in in Samngam, Phopratabchang, Buengnarang & Phothale in Phichit.

– Floodplain of the Yom with normally 1-3 m. deep by flood in September-October.

– Most of vegetative cover over the basin is rice.– Sugarcane is popular growing in upland area.

Flooded photograph interpreted

from satellite was used for contour-lines construction

(adapted from JICA, 1999)

Study area

Contours construction based on flood recorded

3-D landslope, streams & floodplain of the Yom using GIS

SamngamSaingam

Phopratabchang

Phothale

Buengnarang

Saithongpatana

Buengsamakkee

Kanuwora-laksaburi

Wachira-baramee

Total area of those catchments in study area is 1700 sq.km.

Boundary of study area

Hydrological studying

7 Sub-basins as runoff studying, using ArcView GIS

Hydrological studying

AB

E

C

D

Crop name Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

A. HYV rice in lowland floodplainB. HYV-rice in middle zoneC. Plants in upland zone1D. Plants in upland zone2E. Plants in upland zone3

11 2 Flood

1 2 3 1Vegetables

Mungbean corn

sugarcane

Cropping pattern in Phopratabchang as water utilization in the water budget model

Flo

od

ed z

on

e

HYV-rice

HYV-rice

Hydrological studying

• Side-flows 1-hr synthesized unit hydrograph using Nash-model & Gamma function

• Basin characteristics based on US. Army Crop of Engineers method applied with Nash U.H. whereas tp is time to peak discharge, S is channel slope, L and Lc are stream length measure at the longest point and from the centroid of basin, and Ct, Cp, a1, a2 are coefficients getting from linear regression, (Linsley et al., 1988; Jira, 2003).

a), b) Runoff hydrograph synthesized

1-hr UH for the Yom R. by NASH

0.0

0.5

1.0

1.5

2.0

0 10 20 30 40 50

Time, hr

UH

, cu

.m/s

/mm

Samngam-Rangnok

Rangnok-Wangjik

Wangjik-Dannoi

Popatabchang-Phaitapo

Phaitapo-Lamnang

Dannoi-Banglai

Lamnang-Banglai

Banglai-Phothale

US. ACE Basins Characteristics in Research Site

Lag = 1.4317(L.Lc/S^0.5)0.2199

R2 = 0.9886

1

10

100

1 10 100 1000 10000 100000 1000000

LLc/S^0.5

Bas

in L

ag, h

r

a)

b)

Hydrological studying

Daily rainfall over study area in 2001

0

20

40

60

80

100

120

140

160

01/4

/01

01/5

/01

01/6

/01

01/7

/01

01/8

/01

01/9

/01

01/1

0/01

01/1

1/01

01/1

2/01

01/1

/02

01/2

/02

01/3

/02

Ra

infa

ll, m

m/d

St.38062

St.38052

St.38032

St.12102

P3

0

200

400

600

800

1000

1200

1/4/

011/

5/01

31/5

/01

30/6

/01

30/7

/01

29/8

/01

28/9

/01

28/1

0/01

27/1

1/01

27/1

2/01

26/1

/02

25/2

/02

Dis

ch

arg

e, m

3/s

20.00

22.00

24.00

26.00

28.00

30.00

32.00

34.00

36.00

38.00

Wa

ter

Le

ve

l, m

Q-Y17Q-Y5

WL-Y17(u/s of Yom)WL-Y5(d/s of Yom)

Daily rainfall from various rain-gauges in the basin.

Daily river flow from RID’s gagging stations at upstream & downstream of the study area in the Yom R. in 2001

Hydrological studying

Spatially annual rainfall in study area in 2001 using ArcView GIS

St.10102 SaingamSt.39032 Samgam

St.39052 Phothale

St.39062 Phopratabchang

Buengnarang

P3

Hydrological studying

Result of floodplain charac Elevation-Volume-Area

Hydrologic & Hydraulics studying

0

20

40

6080

100

120

140

29.00 34.00 39.00

Flood level, m(MSL)

Are

a, s

q.k

m0

50

100

150

200

Vo

lum

e, M

CM

Vol.MCM

Area, sq.km

0

5

10

15

Inflow

, cu.m/s

0

20

40

60

80

100

Rainf

all, m

m

Rainfall, mm PhairobNongkla Dongsualuang

Result: local streamflow hydrographs

• Total mean annual rainfall in 2001 = 1,146.3 mm• Rainy days = 99, mean daily rainfall = 11.4 mm • Max. temp.=32.6, min. temp.=23.6, Humidity=75.5%,

Sunshine duration=6.9 hr/d, Evap.=4.28 mm/d• Runoff coefficient in rational formula = 0.337• Total Side-flows volume=742.35 MCM or 14.9% of

annual flow at Y17 (Samngam) =4,984 MCM• Return period of max. flood depth in the river

measured at Y17 and analysis based on Gumbel distribution: in year 1995 the return period (Tr) =38yr and max. water level at +38.14 m(MSL), while in 2001 the Tr=5 yr +37.57m, and in 2002 with Tr=50yr (+38.24m)

• Flooded area of 234.231 sq.km occurred in year 2001.

Hydrologic & Hydraulics studying

Simulated result of flood extent on 26 September using HEC-RAS (HEC-2001)

Plan Longitudinal ProfileE

leva

tion

of s

urfa

ce w

ater

, m

(MS

L)

Sta., km (from d/s to u/s)

Distribution of flood flow along the Yom R.Hydraulics studying

Ping river

Yom river

Flo

od

from

rainw

ater

& o

verflow

from

the Y

om

R.

Kampaengphet

Phichit

Saingam

Wachirabaramee

Saithongpatana

Buengsamakkee

PhothaleKhanuworalaksaburi

Phopratabchang

Flood photograph from RADARSAT was used to verify flood extent & flood flow direction on 20 September (GISTDA, 2002)

Flood flow pattern of the Yom R. in PhopratabchangHydraulics studying

Conclusion & Recommendation• Daily flood storage and inundated area in the study site can be

estimated corresponding local inflows, overflow from bankfull of river, existing database from generated contours & basin characteristics using GIS techniques and hydrologic models.

• Most of flood came by overtopping from river bank due to sub-catchments are smaller size than overall river basin area.

• Flood risk map can be processed corresponding GIS, hydrological statistics, and hydrodynamic model, which can be developed and extend to local administration offices and farmer in order to change or shift cropping pattern in floodplain and avoiding flood.

• Infiltration & percolation as losses from surface runoff & flood downward to underground can be considered as flood reduction by temporarily storing into groundwater zone.

• Many sandpits in the basin can be used to reduce flood by infiltration processed which needs to further research.

Thank! to whom supported useful resources i.e. RID, TMD, ESRI, GISTDA, HEC, and ones in ref. (…..).